Method and apparatus for extracorporeal support of premature fetus

ABSTRACT

A system configured to support growth and development of a premature fetus is disclosed. Specifically, a method and apparatus configured to provide extracorporeal support for premature fetuses is disclosed.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/736,825, filed on Dec. 15, 2017, which is a National StageApplication filed under 35 U.S.C. 371 of InternationalPCT/US2016/038045, filed on Jun. 17, 2016, which claims the benefit ofU.S. Provisional Application No. 62/181,861, filed Jun. 19, 2015, andU.S. Provisional Application No. 62/260,251, filed Nov. 26, 2015, thedisclosures of which are incorporated herein by reference in theirentireties.

TECHNICAL FIELD

The present disclosure relates generally to neonatal care. Morespecifically, the present disclosure describes devices, systems, andmethods related to the maintenance of homeostasis in an extremepremature fetus outside of the womb. According to one aspect, thepresent disclosure relates to improving outcomes of premature fetusesborn prior to 28 weeks gestation.

BACKGROUND

Extreme prematurity is the leading cause of infant morbidity andmortality in the United States, with over one third of all infant deathsand one half of cerebral palsy diagnoses attributed to prematurity.Respiratory failure represents the most common and challenging problemassociated with extreme prematurity, as gas exchange in criticallypreterm neonates is impaired by structural and functional immaturity ofthe lungs. Advances in neonatal intensive care have achieved improvedsurvival and pushed the limits of viability of preterm neonates to 22 to24 weeks gestation, which marks the transition from the canalicular tothe saccular phase of lung development. Although survival has becomepossible, there is still a high rate of chronic lung disease and othercomplications of organ immaturity, particularly in fetuses born prior to28 weeks gestation. The development of a system that could supportnormal fetal growth and organ maturation for even a few weeks couldsignificantly reduce the morbidity and mortality of extreme prematurity,and improve quality of life in survivors.

Premature birth may occur due to any one of a multitude of reasons. Forexample, premature birth may occur spontaneously due to preterm ruptureof the membranes (PROM), structural uterine features such as shortenedcervix, secondary to traumatic or infectious stimuli, or due to multiplegestation. Preterm labor and delivery is also frequently encountered inthe context of fetoscopy or fetal surgery, where instrumentation of theuterus often stimulates uncontrolled labor despite maximal tocolytictherapy.

The 2010 CDC National Vital Statistics Report notes birth rates at agestational age of less than 28 weeks in the United States over the pastdecade have remained stable at approximately 0.7%, or 30,000 birthsannually. Similarly, birth rates at gestational ages 28-32 weeks overthe past decade in the United States have been stable at 1.2%, or 50,000births annually. Patients with pulmonary hypoplasia secondary tocongenital diaphragmatic hernia, oligohydramnios, or abdominal walldefects are also significant. The National Birth Defects PreventionNetwork reports an annual incidence of congenital diaphragmatic herniabetween 0.9 to 5.8 per 10,000 live births in the United States, orapproximately 375-2,500 births annually. The incidence of other causesof pulmonary hypoplasia is not well documented.

Respiratory failure remains the major challenge to survival in thecritically premature infant. The development of an extrauterine systemto support ongoing fetal growth and development would represent achanging paradigm in the management of such patients. The development ofan “artificial placenta” has been the subject of investigation for over50 years with little success. Previous attempts to achieve adequateoxygenation of the fetus in animal models have employed traditionalextracorporeal membrane oxygenation (ECMO) with pump support, and havebeen limited by circulatory overload and cardiac failure in treatedanimals. The known systems have suffered from unacceptablecomplications, including: 1) progressive circulatory failure due toafter-load or pre-load imbalance imposed on the fetal heart byoxygenator resistance or by circuits incorporating various pumps; and 2)contamination and fetal sepsis.

Accordingly, despite previous attempts to address the long-felt need fora system to support fetal growth and development for preterm fetuses, asolution has remained elusive.

SUMMARY

The present disclosure provides an extracorporeal system to support amammal, such as a premature fetus. According to one aspect of thedisclosure, the system includes a fluid reservoir having one or moreflexible walls. The fluid reservoir is configured to enclose a fetuswithin a fluid environment and may have an expandable volume and asealable opening. The system may include a fluid supply line configuredto supply a volume of fluid into the fluid reservoir. The system mayfurther include a fluid discharge line configured to discharge fluidfrom the fluid reservoir. The system may include a pumpless pediatricoxygenator configured to exchange oxygen and carbon dioxide in the bloodof the fetus while the fetus is maintained within the fluid reservoir.

According to another aspect of the disclosure, a method of treatment fora premature fetus is provided. The method includes the steps ofproviding a fluid reservoir having one or more flexible walls, fillingthe fluid reservoir with fluid, placing the premature fetus within thefluid reservoir, connecting the premature fetus to a pumpless oxygenatorthat is configured to exchange oxygen and carbon dioxide with the bloodof the premature fetus, or any combination thereof. The method mayfurther include the steps of enclosing the premature fetus within thefluid reservoir, maintaining the premature fetus within the fluidreservoir for a period of time during which the premature fetus can growand/or develop, while the premature fetus is within the fluid reservoirmodifying the fluid reservoir to expand the volume of fluid reservoir,while the premature fetus is within the fluid reservoir infusing fluidinto the fluid reservoir, and while the premature fetus is within thefluid reservoir discharging fluid from the fluid reservoir.

According to another aspect of the disclosure, an extracorporeal systemconfigured to support a mammal, such as a premature fetus, is provided.The system includes a fluid reservoir configured to maintain thepremature fetus in a sealed, liquid environment, a pumpless pediatricoxygenator configured to exchange oxygen and carbon dioxide in the bloodof the premature fetus while the premature fetus is maintained withinthe fluid reservoir, a mechanism configured to manipulate the fluidreservoir, or any combination thereof. The mechanism is configured torotate, translate, or both rotate and translate the fluid reservoirwhile the fetus is maintained in the fluid reservoir so that theposition of the fetus is varied while the fetus is maintained in thefluid reservoir. According to one embodiment, the mechanism includes apair of supports spaced apart from one another and each connected withthe fluid reservoir. The mechanism may include a drive mechanismconfigured to displace the first support relative to the second support,thereby altering the orientation of the fluid reservoir. Additionally oralternatively, the mechanism may include a drive mechanism configured torotate the fluid reservoir, for example about an axis.

According to another aspect of the disclosure, an extracorporeal systemconfigured to support a mammal, such as a premature fetus, is provided.The system includes a fluid reservoir configured to enclose a prematurefetus within a fluid liquid environment. The fluid reservoir includes anexpandable volume, a sealable opening, or both. The system includes afluid supply line configured to supply a volume of fluid into the fluidreservoir, and a fluid discharge line configured to discharge fluid fromthe fluid reservoir. The system includes an oxygenation circuitconfigured to exchange oxygen and carbon dioxide in the blood of thepremature fetus while the premature fetus is maintained within the fluidreservoir. The oxygenation circuit includes a first fluid path from thefetus to an oxygenator and second fluid path from the oxygenator back tothe fetus. The oxygenation circuit may include a by-pass line forre-circulating a portion of blood through the oxygenator. A pump may beprovided along the by-pass line for pumping the portion of blood throughthe by-pass line. The pump may increase the flow rate of the fluidthrough the by-pass line relative to the flow rate of the fluid throughthe first and/or second fluid path.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary and the following detailed description of thepreferred embodiments of the present invention will be best understoodwhen read in conjunction with the appended drawings, in which:

FIG. 1 is an isometric view of an extracorporeal support system in afirst configuration, according to one embodiment;

FIG. 2 is an isometric view of the extracorporeal support systemillustrated in FIG. 1, in a second configuration;

FIG. 3 is an isometric view of a portion of the extracorporeal supportsystem illustrated in FIG. 1;

FIG. 4 is an isometric view of a portion of the extracorporeal supportsystem illustrated in FIG. 1;

FIG. 5 is another isometric view of the portion of the extracorporealsupport system illustrated in FIG. 4, shown from alternate viewingangle;

FIG. 6 is an isometric view of an amniotic fluid circuit of theextracorporeal support system illustrated in FIG. 1, according to oneembodiment;

FIG. 7 is a top plan view of a fetal chamber of the extracorporealsupport system illustrated in FIG. 1, according to one embodiment, thefetal chamber in a closed configuration;

FIG. 8 is an isometric view of the fetal chamber shown in FIG. 7, in anopen configuration;

FIG. 9 is an alternate isometric view of the fetal chamber shown in FIG.7, including an attached restriction ring;

FIG. 10 is a partially exploded isometric view of the fetal chamberillustrated in FIG. 9;

FIG. 11 is a cross-sectional view of the fetal chamber illustrated inFIG. 9, along line 11-11;

FIG. 12 is a diagrammatic view of an amniotic fluid circuit of theextracorporeal support system illustrated in FIG. 1, according to oneembodiment;

FIG. 13 is a diagrammatic view of an amniotic fluid circuit of theextracorporeal support system illustrated in FIG. 1, according toanother embodiment;

FIG. 14 is a diagrammatic view of an oxygenation circuit of theextracorporeal support system illustrated in FIG. 1, according to oneembodiment;

FIG. 15 is a diagrammatic view illustrating the interconnection betweena central controller and a plurality of sensors and controls of theextracorporeal support system illustrated in FIG. 1, according to oneembodiment;

FIG. 16 is a diagrammatic view of an amniotic circuit and an oxygenationcircuit of the extracorporeal support system illustrated in FIG. 1,according to one embodiment;

FIG. 17 is a diagrammatic view of an oxygenation circuit of theextracorporeal support system illustrated in FIG. 1, according toanother embodiment;

FIG. 18 is a diagrammatic view of the transfer of a fetus from in-uteroto the extracorporeal support system illustrated in FIG. 1;

FIG. 19 is an isometric view of a fetal chamber of the extracorporealsupport system illustrated in FIG. 1, according to another embodiment,the fetal chamber in an open configuration;

FIG. 20 is an isometric view of the fetal chamber illustrated in FIG.19, in a closed configuration;

FIG. 21 is a cross-sectional view of a gas blender of the extracorporealsupport system illustrated in FIG. 1, according to one embodiment;

FIG. 22 is a diagrammatic view of a portion of an oxygenation circuit ofthe extracorporeal support system illustrated in FIG. 1, according toone embodiment;

FIG. 23 is an isometric view of a fetal chamber of the extracorporealsupport system illustrated in FIG. 1, according to another embodiment,the fetal chamber in a closed configuration;

FIG. 24 is an isometric view of the fetal chamber of the extracorporealsupport system illustrated in FIG. 23, in an open configuration;

FIG. 25 is an isometric view of a fetal chamber and a mechanismconfigured to manipulate the fetal chamber of the extracorporeal supportsystem illustrated in FIG. 1, according to one embodiment;

FIG. 26 is an isometric view of a fetal chamber and a heating elementconfigured to change the temperature within the fetal chamber of theextracorporeal support system illustrated in FIG. 1, according to oneembodiment;

FIG. 27 is an isometric view of a fetal chamber of the of theextracorporeal support system illustrated in FIG. 1, according toanother embodiment;

FIG. 28 is an isometric view of a portion of the fetal chamberillustrated in FIG. 27;

FIG. 29 is an isometric view of the fetal chamber illustrated in FIG.27, and a mechanism configured to manipulate the fetal chamber, both thefetal chamber and the mechanism in a closed configuration;

FIG. 30 is an isometric view of the fetal chamber and mechanismillustrated in FIG. 29, both the fetal chamber and the mechanism in anopen configuration;

FIG. 31 is an isometric view of a fetal chamber of the of theextracorporeal support system illustrated in FIG. 1, according toanother embodiment, the fetal chamber in a closed configuration;

FIG. 32 is an isometric view of the fetal chamber illustrated in FIG.31, the fetal chamber in a closed configuration;

FIG. 33 is an isometric view of a portion of the fetal chamberillustrated in FIG. 31;

FIG. 34 is an isometric view of the fetal chamber illustrated in FIG.31, according to another embodiment;

FIG. 35 is another isometric view of the fetal chamber illustrated inFIG. 34;

FIG. 36 is an isometric view of the fetal chamber illustrated in FIG.31, according to another embodiment;

FIG. 37 is another isometric view of the fetal chamber illustrated inFIG. 36;

FIG. 38 is an isometric view of a portion of the extracorporeal supportsystem illustrated in FIG. 1, according to one embodiment;

FIG. 39 is an isometric view of an extracorporeal support system in afirst configuration, according to another embodiment, the extracorporealsupport system in a closed configuration;

FIG. 40 is a side elevation view of the extracorporeal support systemillustrated in FIG. 39;

FIG. 41 is an isometric view of the extracorporeal support systemillustrated in FIG. 39, in an open configuration;

FIG. 42 is a diagrammatic view of a fetal chamber of the extracorporealsupport system, according to one embodiment;

FIG. 43 is a first graph illustrating experimental results;

FIG. 44 is a second graph illustrating experimental results;

FIG. 45 is a third graph illustrating experimental results;

FIG. 46 is a fourth graph illustrating experimental results;

FIG. 47 is a fifth graph illustrating experimental results;

FIG. 48 is a sixth graph illustrating experimental results;

FIG. 49 is a seventh graph illustrating experimental results;

FIG. 50 is first table illustrating experimental results;

FIG. 51 is an eighth graph illustrating experimental results;

FIG. 52 is a ninth graph illustrating experimental results;

FIG. 53 is a tenth graph illustrating experimental results;

FIG. 54 is a eleventh graph illustrating experimental results;

FIG. 55 is a second table illustrating experimental results;

FIG. 56 is a third table illustrating experimental results;

FIG. 57 is a twelfth graph illustrating experimental results;

FIG. 58 is a thirteenth graph illustrating experimental results;

FIG. 59 is a fourteenth graph illustrating experimental results;

FIG. 60 is a fourth table illustrating experimental results;

FIG. 61 is a fifteenth graph illustrating experimental results;

FIG. 62 is a sixteenth graph illustrating experimental results;

FIG. 63 is a seventeenth graph illustrating experimental results;

FIG. 64 is a fifth illustrating experimental results;

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Aspects of the disclosure will now be described in detail with referenceto the drawings, wherein like reference numbers refer to like elementsthroughout, unless specified otherwise. Referring to FIGS. 1 to 5 anextracorporeal support system 10 may be configured to treat prematurefetuses (referred to herein as “fetuses”). The system 10 includes afetal chamber 100 configured to house a fetus 5, an amniotic fluidcircuit 200 configured to provide a flow of amniotic fluid to the fetalchamber 100, and an oxygenation circuit 400 configured to remove carbondioxide from the fetus's blood and supply oxygen to the fetus's blood.The system 10 is configured to maintain the fetus 5 in the fetal chamber100 immersed in amniotic fluid that is part of the amniotic fluidcircuit 200. The system 10 is further configured such that theoxygenation circuit 400 provides adequate gas exchange for the fetus 5to sustain life. In this way, the system 10 provides an environmentsimilar to an intrauterine environment to facilitate continued growthand development of the fetus 5. The system 10 may include a cart 50 thatfacilitates monitoring, caring for, and transporting the fetus 5 withina medical facility. According to one embodiment, a central controller700, such as a microprocessor may be provided to receive signals fromvarious elements of the system 10 and control operation of varioussubassemblies of the system 10. The details of each of the subsystemswill be described in greater detail below.

The fetal chamber 100 includes an enclosed fluid chamber configured tohouse the fetus 5 in a sterile liquid environment. The fetal chamber 100is configured to provide a fluid environment that allows fetal breathingand swallowing to support normal lung and gastrointestinal development,as well as providing fluid and electrolyte balance.

According to one aspect of the disclosure, the fetal chamber 100 isconfigured to generally conform to the shape of the fetus 5, and tominimize areas of stagnation that could promote bacterial growth thatcould lead to infection. As shown in the illustrated embodiment thefetal chamber 100 may be configured to generally conform to the shape ofa human fetus 5. According to another embodiment, for example as shownin FIG. 31, the fetal chamber 100 may be configured to generally conformto the shape of a non-human fetus, such as a lamb fetus.

Referring to FIGS. 7 to 11, according to one aspect of the disclosure,the fetal chamber 100 includes rigid walls to provide a rigid chamber.According to another aspect of the disclosure, as shown in theillustrated embodiments, the fetal chamber 100 includes one or moreflexible walls 120. As shown in the illustrated embodiment, the fetalchamber 100 may include a sac or bag formed of flexible material, suchas a plastic film, for example a flexible polyethylene film. The filmmay incorporate an antimicrobial element to control the growth andspread of microbes in the fetal chamber 100. The antimicrobial elementmay be organic or inorganic. According to one aspect of the disclosurethe antimicrobial element includes an inorganic element such as silver.According to one example, the one or more flexible walls 120 of thefetal chamber 100 are made of a material including metallocenepolyethylene film, for example about 80 micrometer thick and containing2% silver cation as an antimicrobial element.

Referring to FIGS. 7 to 11, the fetal chamber 100 may include agenerally rigid frame 110 that supports one or more flexible walls 120.The rigid frame 110 may be formed of a variety of materials, including,but not limited to plastic or metal. The flexible walls 120 are fixedlyconnected with the rigid frame 110, for example by welding or anadhesive. The flexible walls 120 allow a volume defined by the fetalchamber 100 to expand and contract. According to one aspect of thedisclosure, the fetal chamber 100 is configured to expand as the fetus 5enclosed within the fetal chamber 100 grows, allowing the volume of thechamber to be increased without opening or changing the fetal chamber100 of the system 10. According to one aspect of the disclosure thefetal chamber 100 may include a single flexible wall 120. According toanother aspect of the disclosure, the fetal chamber 100 may include aplurality of flexible walls 120, for example upper and lower flexiblewalls 120 fixedly connected with the rigid frame 110.

As shown in the illustrated embodiment, the fetal chamber 100 includes asealable opening configured to allow the fetus 5 to be placed into thefetal chamber 100 in an open configuration (as shown in FIG. 8) and thensealed once the fetus 5 is inside the fetal chamber 100 in a closedconfiguration (as shown in FIG. 7). According to one aspect of thedisclosure, the fetal chamber 100 may have a clamshell design in whichthe fetal chamber 100 includes an upper half 102 and a lower half 104connected by at least one hinge 106 so that the upper half 102 ispivotable relative to the lower half 104. As shown in the illustratedembodiment, the fetal chamber 100 may include a seal 116, such as anelastomeric material (for example resilient plastic, urethane or rubber)extends around at least a portion, for example an entirety, of theperiphery of the upper half 102, the lower half 104, or both. The fetalchamber 100 may further include a lip 118 on either the upper half, thelower half, or both, the seal configured to cooperate with the seal 116on the opposite (upper or lower) half of the fetal chamber 100 to form afluid-tight seal when the fetal chamber 100 is in the closedconfiguration. The fetal chamber 100 preferably includes a mechanism 114configured to retain the fetal chamber 100 in the closed configuration.For instance, the fetal chamber 100 may include one or more latchesconfigured to releasably lock the upper half 102 of the fetal chamber100 to the lower half 104 of the fetal chamber 100 to maintain the fetalchamber 100 in the closed, fluid-tight configuration.

A first orifice at a first end 108 of the fetal chamber 100 forms aninlet 142 configured to receive amniotic fluid into the fetal chamber100. A second orifice at a second end 109 of the fetal chamber 100 formsan outlet 144 configured to discharge amniotic fluid from the fetalchamber 100. In the embodiment shown in FIG. 7, the fetal chamber 100 iselongated to accommodate a human fetus 5. As shown in the illustratedembodiment, a length of the fetal chamber 100, measured for example fromthe inlet 142 to the outlet 144, may be greater than a width of thefetal chamber 100, measured in a direction perpendicular to the length.The first end 108 and the second end 109 may taper inwardly to minimizelocations within the fetal chamber 100 where amniotic fluid maystagnate. As shown in the illustrated embodiment, the fetal chamber 100is an ovate or elliptical shape having a major axis along the length ofthe fetal chamber 100 and the minor axis along the width of the fetalchamber 100.

According to one aspect of the disclosure, the fetal chamber 100 isconfigured to receive the fetus 5 such that a head of the fetus 5 isadjacent the inlet 142. Positioning the fetus 5 within the fetal chamber100 such that the head of the fetus 5 is adjacent the inlet 142 mayallow more efficient removal of waste generated by the fetus 5 from thefetal chamber 100.

The fetal chamber 100 may include a plurality of sensors configured tomonitor conditions within the fetal chamber 100. For instance, the fetalchamber 100 may include one or more temperature sensor configured todetect fluid temperature within the fetal chamber 100. In the presentembodiment, the fetal chamber 120 includes at least one, for example apair of, thermocouples 130 configured to monitor fluid temperaturewithin the fetal chamber 100. Additionally, one or more fluid pressuresensors 140 may be positioned within the fetal chamber 100. For example,as shown in the illustrated embodiment, a fluid pressure sensor 140 maybe positioned within the fetal chamber 100 adjacent the outlet 144, thefluid pressure sensor configured to monitor fluid pressure within thefetal chamber 100. Alternatively, the fluid pressure sensor 140 may bemounted within the outlet 144 such that the fluid pressure sensor isconfigured to monitor fluid pressure of fluid discharging from the fetalchamber 100.

The fetal chamber 100 may also include one or more sealed openingsconfigured to provide access an interior of the fetal chamber 100.According to one aspect of the disclosure, the one or more sealedopenings may include an upper port 122, formed in the upper half 102 ofthe fetal chamber 100 for example, and a lower port 124, formed in thelower half 104 of the fetal chamber 100. As shown in the illustratedembodiment, at least one of the upper port 122 and the lower port 124are sealed by a valve that provides one way flow. For example the valvemay be configured to permit access into the fetal chamber 100 whileimpeding fluid flow out of the fetal chamber 100. The valves may be anyof a variety of valves configured to control flow of fluid. According toone example, the valves may be duck bill valves. The upper port 122 andthe lower port 124 are each configured to allow insertion of a suctiondevice into the fetal chamber 100, for example to evacuate air bubbles,stool contamination, and other contaminates from the fetal chamber 100.

The fetal chamber 100 may further include an orifice 135 configured toprovide access for conduits or other portions of the oxygenation circuit400 described further below. The fetal chamber may include a sealconfigured to seal the orifice 135 when the fetal chamber is in theclosed configuration.

The fetal chamber 100 may be formed with a predetermined fixed volumethat is sufficiently large to accommodate the fetus 5 after it has grownfor several weeks or months. In this way, the fetal chamber 100 isconfigured to maintain the fetus 5 within the fetal chamber 100 duringthe entire period of development without the fetus 5 growing too largefor the fetal chamber 100. Alternatively, the fetal chamber 100 mayinclude a variable volume chamber so that the fetal chamber volume canbe sized to the minimum volume necessary to support the fetus 5 when thefetus 5 is initially enclosed within the fetal chamber 100. As the fetus5 grows, the fetal chamber 100 is configured to be expanded withoutopening the fetal chamber 100.

The system 10 may include one or more mechanisms configured to vary thevolume of the fetal chamber 100. According to one aspect of thedisclosure, the system 10 includes one or more restriction rings 150configured to constrain the flexible walls 120 of the fetal chamber 100,thereby reducing the volume of the fetal chamber 100. The restrictionring 150 may be configured to releasably attach to the frame 110 of thefetal chamber 100 so that the restriction ring 150 can be attached anddetached from the fetal chamber 100.

As shown in the illustrated embodiment, the restriction ring 150 may beshaped generally similarly to the shape of the flexible wall 120. Therestriction ring may include an inner protrusion 152 extending around atleast a portion of an interior edge of the restriction ring 150. Whenattached to the frame 110, the inner protrusion 152 of the restrictionring 150 is spaced inwardly from an outer edge of the flexible wall 120.The inner protrusion 152 of the restriction ring 150 applies inwardpressure against the flexible wall 120 thereby restricting outwarddisplacement of the flexible wall 120. As a result, the restriction ring150 restricts the internal volume of the fetal chamber 100.

The restriction ring 150 may include a plurality of latches or clips154, for example formed around a periphery of the restriction ring 150configured to releasably connect the restriction ring 150 to the chamberframe 110. As shown in the illustrated embodiment, the clips 154 areconfigured to snap over tabs 155 formed on the chamber frame 110 toretain the restriction rings 150 against the outward force of fluidpressure within the fetal chamber 100 pushing the flexible wall 120outwardly. According to one embodiment, the system 10 is devoid of arestriction ring 150. According to another embodiment, the system 10includes a single restriction ring 150. According to another embodiment,the system 10 may include a plurality of restriction rings 150, forexample a first restriction ring 150 configured to be attached to theupper half 102 of the fetal chamber 100 to restrict the upper flexiblewall 120 and a second restriction ring 150 is configured to be attachedto the lower half 104 of the fetal chamber 100 to restrict the lowerflexible wall 120. As the fetus 5 grows, the restriction ring(s) 150 canbe detached from the fetal chamber 100 to allow the flexible walls 120to expand outwardly, thereby increasing the internal volume of the fetalchamber 100. Additionally, the system 10 may include a plurality ofdifferent sized restriction rings 150, with each ring allowing theflexible walls 120 to expand to a different extent. In this way, as thefetus 5 grows, the volume of the fetal chamber 100 can be increasedincrementally over time.

Referring to FIGS. 4 to 6, the amniotic circuit 200 of the system 10 isconfigured to provide a fluid, for example a sterile fluid, to the fetalchamber 100 and is further configured to discharge the fluid from thefetal chamber 100. According to one aspect of the disclosure, theamniotic circuit 200 is configured to control flow of the fluid enteringthe fetal chamber 100 and being discharged from the fetal chamber 100 tomaintain fluid pressure in the fetal chamber 100 within a pre-determinedrange. The amniotic circuit 200 may be a closed circuit in which thefluid discharges from the fetal chamber 100, is processed by filtrationand sterilization prior to being recycled back into the fetal chamber100. However, as shown in the illustrated embodiment, the amnioticcircuit 200 may be an open circuit in which the fluid flows from asupply tank 210 which houses a reservoir of fresh amniotic fluid intothe fetal chamber 100 and the fluid exits the fetal chamber 100 and isdischarged into a waste tank 220. The amniotic circuit 200 also mayinclude one or more elements configured to process the fluid prior toinjecting the fluid into the fetal chamber 100 as discussed furtherbelow.

It should be understood that the terms “fluid” and “amniotic fluid” isused to refer to the fluid that is used to fill the fetal chamber 100.The composition of the fluid may vary depending on a variety of factors.For instance, the amniotic fluid may include primarily water, such asdistilled water, and may be mixed with a variety of elements, such aselectrolytes (for example, but not limited to, sodium chloride, sodiumbicarbonate, potassium chloride, calcium chloride, or any combinationthereof) dissolved in solution to mimic the ionic concentration ofnaturally occurring amniotic fluid for a fetus in utero. Additionally,glucose, amino acids, lipids, essential vitamins, minerals, traceelements, or any combination thereof may be added to the amniotic fluid.Accordingly, the term amniotic fluid in this specification does notrefer to a solution having a particular composition, but instead refersto the fluid used to fill the fetal chamber 100.

The amniotic circuit 200 includes the supply tank 210 configured tostore a reservoir of unused amniotic fluid. The supply tank 210 mayinclude a portable tank 210 a configured to be transported on the cart50, a larger tank 210 b configured to remain in a particular area andhaving a substantially larger volume configured to provide a supply ofamniotic fluid for a longer period of time than the portable tank 210 a,or both. The amniotic circuit 200 includes the waste tank 220 configuredto collect amniotic fluid discharged from the fetal chamber 100. Thewaste tank 220 may include a portable tank 220 a configured to betransported on the cart 50, a larger tank 220 b configured to remain ina particular area and having a substantially larger volume configured toreceive used amniotic fluid over a longer period of time than theportable tank 220 a. For instance, the larger tanks 210 b and 220 b mayhave volumes that are at least one order of magnitude larger than theportable tanks 210 a and 220 a.

Referring to FIGS. 4 to 8 and 12, fluid flows from the supply tank 210to the fetal chamber 100 through a supply line 300. The supply lineforms a fluid-tight connection with the inlet 142 of the fetal chamber.A discharge line 320 forms a fluid-tight seal with the outlet 144 of thefetal chamber 100 and thereby provides a fluid path for fluiddischarging from the fetal chamber 100. The system 10 may include aheater 270 configured to provide heat to the amniotic fluid and therebymaintain the amniotic fluid at a selected temperature, for example atemperature corresponding to the temperature of amniotic fluid in utero.The heater 270 may be part of the amniotic circuit 200, for example theheater 270 may be provided in the supply tank 210 so that the reservoirof amniotic fluid is maintained at the selected temperature. As shown inthe illustrated embodiment, the heater 270 is positioned inline betweenthe supply tanks 210 and the fetal chamber 100.

According to one aspect of the disclosure, the heater may 270 be anelectric heater having a control configured to vary the heat output ofthe heater to heat the fluid to the selected temperature as the amnioticfluid flows through the heater 270. It may be desirable to preventdirect contact between the fluid heater 270 and the supply tank 210.Accordingly, the heater 270 may be configured to receive a disposablefluid pathway, such as a cartridge, that allows heat exchange betweenthe heater 270 and the fluid without the heater 270 coming in contactwith the fluid. In this way, the cartridge can be replaced each time thesystem 10 is used to prevent cross-contamination of the heater 270 fromthe fluid used for one fetus 5 with the fluid used for a subsequentfetus 5.

The amniotic circuit 200 may also include one or more filters 250configured to filter the amniotic fluid prior to entering the fetalchamber 100. As shown in the illustrated embodiment, a plurality of thefilters 250, for example three micropore filters, may be included,arranged in parallel, and positioned in-line between the supply tank 210and the fetal chamber 100, for example between the heater 270 and thefetal chamber 100. Other numbers, arrangements, and positions of thefilters 250 are also considered part of the present disclosure.

According to one aspect of the disclosure, the system 10 may include afluid control system 228 configured to control flow of the fluid to andfrom the fetal chamber 100. The fluid control system 228 may be designedto provide a constant flow of fluid to the fetal chamber 100 whilemaintaining a generally constant fluid pressure within the fetal chamber100. In particular, the fluid pressure is maintained within apredetermined range depending on various characteristics, such as thetype and/or size of the fetus 5 in the fetal chamber 100.

In the present instance, the supply tank(s) 210 are maintained underpressure by a pressurized gas. For instance, the large tank may beconnected with a source of pressurized air such as a central medical airsupply commonly used in medical facilities. Additionally, a local supplyof pressurized gas may be provided. For instance, a portable tank 230 ofpressurized gas may be provided to pressurize the fluid in portable tank210 to drive the amniotic fluid toward the fetal chamber 100. It may bedesirable to provide a pressure regulator 232, such as an electronicpressure regulator to regulate the gar pressure of the gas pressurebeing supplied to the supply tanks 210 a and 210 b. In the presentinstance, a first pressure regulator 232 a is provided inline betweenthe portable gas tank 230 and the portable supply tank 210 a and asecond pressure regulator 232 b is provided inline between the centralair supply and the large tank 210 b.

According to one aspect of the disclosure, the system 10 may include afluid controller configured to control flow of pressurized fluid to thefetal chamber 100. As shown in the illustrated embodiment, the amnioticcircuit 200 may include a control valve 242 inline between the supplytank(s) 210 and the fetal chamber 100. Additionally a fluid flow meter244 may be provided inline upstream from the fetal chamber 100 to sensethe flow rate of the amniotic fluid to the fetal chamber 100. The fluidflow meter 244 may be configured to provide signals to the centralcontroller 700, which in turn controls the control valve 242 to regulateflow of the amniotic fluid to the fetal chamber 100 in response tosignals from the fluid flow meter 244.

The system 10 may include a manifold 280 configured to control whetherthe amniotic fluid is supplied from the portable tank 210 a or the largetank 210 b. According to one aspect of the disclosure the manifold 280may include a control valve configured to control flow of the fluid fromthe supply tank(s) 210. The control valve may be manual or it may beelectronically controlled. In a first position, the valve disconnectsfluid flow from the portable tank 210 a and connects fluid flow from thelarge tank 210 b. In a second position, the valve disconnects fluid flowfrom the large tank 210 b and connects fluid flow from the portable tank210 a. In a third position, the valve disconnects both the portable tank210 a and the large tank 210 b to prevent flow of the amniotic fluidfrom either tank so that the amniotic circuit 200 can be purged.

In the foregoing description, the amniotic fluid is driven toward thefetal chamber 100 using pressurized gas to create a pressuredifferential that urges the amniotic fluid toward the fetal chamber 100.It should be understood however, that alternate elements can be used todrive the amniotic fluid toward the fetal chamber 100. For instance, apump may be provided that pumps the amniotic fluid from the tank(s) 210to the fetal chamber 100. The pump may be a pump that does not directlycontact the fluid, such as a peristaltic pump. Additionally, the pumpmay be controlled by the central controller 700 to automatically controlthe pressure and flow rate of the fluid flowing into the fetal chamber100.

As shown in FIG. 12, the amniotic circuit 200 may also include one ormore valves in-line with the supply line 300 to prevent back flow of thefluid from the fetal chamber 100 back toward the supply tanks 210 a and210 b. For instance, the amniotic circuit 200 may include one or morecheck valves 246 to prevent the back flow of fluid from the fetalchamber toward the supply tanks.

The discharge of the fluid from the fetal chamber 100 may be controlledby flow of the fluid entering the fetal chamber 100 from the supply tank210 so that discharge of the fluid is dependent on fluid pressure in thefetal chamber 100 and flow rate of the fluid into the fetal chamber 100.According to another embodiment, discharge of the fluid from the fetalchamber 100 is controlled independently from the infusion of the fluidinto the fetal chamber 100. For example the system 10 may include adischarge pump 240 configured to control flow of the fluid out of thefetal chamber 100. Operation of the discharge pump 240 may be controlledby the central controller 700 based on signals received from variouselements of the system 10.

For example, a pressure sensor may sense fluid pressure in the fetalchamber 100 and the discharge pump 240 may operate to withdraw an amountof the fluid from the fetal chamber 100 to maintain a constant fluidpressure within a desired pressure range in the fetal chamber 100.Additionally, the system 10 may include one or more turbidity sensors350 (also referred to as a turbidity meter) configured to detectturbidity of the fluid in the fetal chamber 100 and/or the dischargeline 320. In response to turbidity sensed by the sensor 350, thedischarge pump 240 may adjust the flow rate of the fluid discharged fromthe fetal chamber 100. For instance, an increase in turbidity in thefluid may be indicative of contaminants in the fetal chamber 100, suchas microbes or stool from the fetus 5. To flush the contaminants fromthe fetal chamber 100, the discharge pump 240 may increase the rate offluid flow out of the fetal chamber 100. In response, the flow rate ofthe fluid being supplied to the fetal chamber from the supply tank 210is increased to maintain a constant fluid level within the fetal chamber100.

Referring now to FIGS. 7 to 11 and 14, the system 10 includes anoxygenation circuit 400 configured to provide gas transfer between thefetus's blood and an oxygenator 410 to provide oxygen to and removecarbon dioxide from the fetus's blood. The oxygenation circuit 400 canbe connected with the fetus 5 in a venous/venous arrangement.Alternatively, the oxygenation circuit 400 may be connected with thefetus 5 in an arterial/venous arrangement. In the present instance,cannulae are placed in the great neck vessels (e.g., carotid) of thefetus 5 to connect the circulatory system of the fetus 5 to theoxygenator 410. The placement in the great neck vessels may avoid issuesof vasospasm and cannula instability in umbilical vessels. An externalportion of the cannulas may be fitted with a sleeve (e.g., to permitincreased tension of the stabilizing sutures). The sleeve may be made ofsilicone and may be, for example, about 1-10 cm in length, particularlyabout 3-5 cm in length. The cannulae may be sutured to the fetus 5 (forexample via the fitted sleeve) to secure the cannulae to the neck of thefetus 5.

The oxygenator 410 is connected with the fetus 5 via two fluid lines: adrain line 440 and an infusion line 445. Blood flows from the fetus 5though the drain line 440 to the oxygenator 410. The blood then flowsthrough the oxygenator 410 and returns to the fetus 5 via the infusionline 445. The drain line 440 and infusion line 445 pass through theoxygenator orifice 135 in the fetal chamber 100. According to one aspectof the disclosure the drain line 440 and the infusion line 445 passthrough apertures in a mounting block 450 and the mounting block 450 isconfigured to be retained in the orifice 135 of the fetal chamber 100.According to one aspect of the disclosure, the mounting block 450 isformed of a resilient material that forms a seal with the frame 110 whenthe upper half 102 and the lower half 104 of the fetal chamber 100 abutsuch that the fetal chamber 100 is in the closed configuration. In thisway, the mounting block 450 provides a fluid-tight seal to impedeleakage of the amniotic fluid from the fetal chamber 100.

As shown in the illustrated embodiment, the oxygenator 410 may bemounted onto a platform 460 adjacent the fetal chamber 100 so that thelength of the drain line 440 and the infusion line 445, to and from theoxygenator 410 respectively, is minimized. For instance, in accordancewith one aspect of the disclosure, the drain line 440 and the infusionline 445 are less than 18 inches long combined, and preferably are notgreater than 12 inches long combined. By minimizing the length of thedrain line 440 and the infusion line 445, the volume of blood requiredto prime the oxygenation circuit 400 is minimized. It may be desirableto line the drain line 440 the infusion line 445, or both withanti-clotting measures/compounds (for example, but not limited to,immobilized polypeptide, heparin, or both). The oxygenation circuit 400may be primed with, for example, maternal blood, blood of the fetus 5,or both. Priming of the oxygenation circuit 400 with hemoglobin from thefetus 5 may result in optimal oxygen exchange in the oxygenation circuit400. Because the fetal oxygen dissociation curve is shifted to the leftcompared to the adult oxygen dissociation curve, fetal arterial oxygenpressures are lower than adult arterial oxygen pressures. In aparticular embodiment, the blood in the oxygenation circuit 400 includesheparin.

The platform 460 is configured to support the oxygenator 410. Accordingto one example, the platform 460 includes a boss onto which theoxygenator 410 is configured to snap to retain the oxygenator 410 inposition. The platform 460 may be connected with the frame 110 of thefetal chamber 100, for example the platform 460 may be integrally moldedwith the frame 110.

According to one aspect of the disclosure, the oxygenation circuit 400includes a sweep gas connected with the oxygenator 410, the sweep gasconfigured to facilitate gas transfer between the oxygenator 410 and theblood of the fetus 5. The gas transfer is affected by the composition ofthe sweep gas and the flow rate of the sweep gas through the oxygenator410. As shown in FIG. 14, two gases, for example an oxygen source 520and an air source 530, are blended together in a gas blender 540 thatblends the oxygen and the air to form the sweep gas. The details of thegas blender are illustrated in FIG. 21. The two gases may be supplied bya high volume gas reservoir, such as wall lines connected with a centralgas supply configured to provide gas to the reservoir. Alternatively,the two gases maybe supplied from smaller gas reservoirs, such as aportable oxygen tank 520 and a portable air tank 530 that are mounted onthe cart 50 so that the system 10 can provide sweep gas to theoxygenator 410 while the system 10 is conveyed from one area of amedical facility to another area of the medical facility.

The oxygenation circuit 400 may include a first control valve 525configured to control whether the wall source oxygen supply or theportable oxygen tank 520 is connected with the gas blender 540. Theoxygenation circuit 400 may include a second control valve 535configured to control whether the wall source air or the portable airtank 530 is connected with the gas blender 540. The oxygenation circuit400 may include one or more pressure sensors 522 positioned inline withthe oxygen supplies and one or more pressure sensors 532 are positioninline with the air supplies so that the pressure sensors 522 and 532sense the gas pressure of the gases being fed to the gas blender 540.

The oxygenation circuit 400 may include a heater 550 positioned inlinebetween the gas blender 540 and the oxygenator 410, the heater 550configure to heat the sweep gas so that the temperature of the sweep gasis maintained within a predetermined range. The oxygenation circuit 400may include a fluid flow meter 562 configured to monitor the flow rateof the sweep gas exiting the heater 550 and a sweep gas analyzer 565configured to analyze one or more characteristics of the gas enteringthe oxygenator 410. The oxygenation circuit 400 may include an exhaustgas analyzer 570 configured to analyze one or more characteristics ofthe gas discharged by the oxygenator 410. For instance, the gasanalyzers 565 and 570 may be configured to measure the oxygen content ofthe sweep gas and the exhaust gas, respectively.

The oxygenation circuit 400 further includes a pair of fluid pressuresensors configured to detect the fluid pressure of the blood enteringthe oxygenator 410 and the fluid pressure of the blood exiting theoxygenator 410. Specifically, a first pressure sensor 590 may bepositioned in-line with the drain line 440 and a second pressure sensor592 may be positioned in-line with the infusion line 445. In this way,the fluid pressure drop over the oxygenator 410 can be continuouslymonitored. Additionally, a fluid flow meter 595 may be positionedin-line with the infusion line 445 to monitor the flow rate of the bloodreturning to the fetus 5 from the oxygenator 410.

The oxygenation circuit 400 may include one or more ports 580, which maybe utilized to withdraw blood samples for analysis or the ports 580 maybe used to inject or infuse medicine or nutrition directly into theblood. For instance, one of the ports 580 may be configured tofacilitate injection of medication such as antibiotics or sedatives intothe blood. Similarly, another of the ports 580 may be configured tofacilitate injection of nutrition such as total parental nutrition (TPN)into the blood.

In accordance with one aspect of the disclosure, the fetus's heart isused to drive blood flow through the oxygenation circuit 400, so a pumpis not used to drive the blood through the oxygenation circuit 400. Inother words, according to one aspect of the disclosure, the oxygenationcircuit 400 is a pumpless circuit. The use of a pumpless system avoidsexposure of the fetus's heart to excess preload encountered innon-pulsatile pump-assisted circuits. The pumpless system also permitsintrinsic fetal circulatory regulation of flow dynamics. The oxygenator410 preferably has very low resistance, low priming volume, lowtransmembrane pressure drops, and provides efficient gas exchange. In aparticular embodiment, the oxygenator 410 has a pressure drop of lessthan about 50 mmHg or about 40 mmHg at 1.5 l/min of blood flow. In aparticular embodiment, the priming volume of the oxygenator 410 is lessthan about 100 ml and in particular is less than about 85 ml. In aparticular embodiment, the oxygenator 410 has a blood flow range up toabout 2.0 l/min, about 2.5 l/min, about 2.8 l/min, or greater. In aparticular embodiment, the oxygenator 410 has a gas transfer rate ofabout 150 ml/min, about 160 ml/min, about 180 ml/min, or greater for 02.In a particular embodiment, the oxygenator 410 is a hollow fibermembrane oxygenator (for example, but not limited to, a polymethylpentene hollow fiber membrane oxygenator). The oxygenator 410 may belined with anti-clotting measures/compounds such as immobilizedpolypeptide and/or heparin). An exemplary oxygenator is the Quadrox-iD™pediatric oxygenator (Maquet; Wayne, N.J.).

The system 10 may be configured for use with fetuses, including term andpreterm fetuses. The preterm fetus may be a premature fetus (forexample, less than 37 weeks estimated gestational age, particularly 28to 32 weeks estimated gestational age), extreme premature fetuses (24 to28 weeks estimated gestational age), or pre-viable fetuses (20 to 24weeks estimated gestational age). The gestation periods are provided forhumans, though corresponding preterm fetuses of other animals may beused. In a particular embodiment, the preterm fetus has no underlyingcongenital disease. In a particular embodiment, the term or pretermfetus has limited capacity for pulmonary gas exchange, for example, dueto pulmonary hypoplasia or a congenital anomaly affecting lungdevelopment, such as congenital diaphragmatic hernia. In a particularembodiment, the subject is a preterm or term neonate awaiting lungtransplantation, for example, due to congenital pulmonary disease (e.g.,bronchoalveolar dysplasia, surfactant protein B deficiency, and thelike). Such transplantation surgeries are currently rarely performed inthe United States. However, the number of transplantation surgeries maybe increased with the more stable method for pulmonary support providedby the instant invention. The fetus 5 may also be a candidate for exutero intrapartum treatment (EXIT) delivery, including patients withsevere airway lesions and a long expected course before definitiveresection. The fetus 5 may also be a fetal surgical or fetoscopicprocedure patient, particularly with preterm labor precipitating earlydelivery. According to one aspect of the disclosure the system 10 isconfigured such that the fetus 5 may be maintained in the system 10 foras long as needed (for example, for days, weeks or months, until thefetus 5 is capable of life without the system 10).

Referring to FIGS. 8, 24, 25, 27, 29, 30, and 38, according to oneaspect of the disclosure, the system 10 may be configured to displacethe fetal chamber 100 so that the fetus 5 is not continuously maintainedin the same orientation, for example with respect to the ground.Specifically, the system 10 may include a chamber displacement system600 configured to displace the fetal chamber 100. The chamberdisplacement system 600 may be operable to tilt and/or rotate the fetalchamber 100 to alter the orientation of the fetus 5 and the fetalchamber 100 with respect to other portions of the system 10, for examplethe cart 50.

According to one embodiment, the displacement system 600 may beconfigured to raise, lower, or both, one or both ends 108, 109 of thefetal chamber 100 to tilt the fetal chamber 100 relative to a horizontalorientation, for example parallel to the ground. Specifically, each end108, 109 of the fetal chamber 100 may be supported by an arm of thedisplacement system 600. Each of the arms can be independently extendedor retracted to raise or lower each end of the fetal chamber 100. Inthis way, the fetal chamber can be tilted.

Alternatively, for example as illustrated in FIGS. 8, 25 and 38, thechamber displacement system 600 includes a cradle 610 having first andsecond supports 620, 625 that support the first and second ends 108, 109of the fetal chamber 100. More specifically, the chamber frame 110 mayinclude a first cradle mount 112 at the inlet 142 and a second cradlemount 112 at the outlet 144. The cradle mounts 112 mate with the arms ofthe cradle 610 to permit rotation of the fetal chamber about an axis 604that extends through the cradle mounts 112. Additionally, the cradle 610may be pivotable so that a first end of the cradle 610 may be pivotedupwardly relative to a second end of the cradle 610 to tilt the fetalchamber 100 relative the horizon.

The system 10 may be configured such that chamber displacement system600 may be manually or automatically actuated. For instance, in a manualconfiguration the fetal chamber 100 is configured to be manually rotatedabout the axis 604, for example a horizontal axis by an operator.Similarly, the cradle 610 may be displaced vertically by pivoting oneend of the cradle 610 upwardly as shown in FIG. 38. Alternatively, thechamber displacement system 600 may include a drive motor configured todrive rotation of the fetal chamber 100 about the axis 604, for examplea horizontal axis. Similarly, the drive motor may drive the cradle 610to tilt the cradle 610 vertically.

Referring to FIGS. 1 to 3, the system 10 may include a cart 50 such thatthe system 10 is transportable from one area in a medical facility, suchas an operating room, to another area in the medical facility, such as aneonatal care center, without needing to remove the fetus 5 from thefetal chamber 100.

The cart 50 may incorporate any of a plurality of elements of the system10. For instance, the cart 50 may include a hood 60 configured toenclose and/or cover the fetal chamber 100 to limit access to the fetalchamber 100. The hood 60 may be pivotable or the hood 60 may betranslatable, for example by lifting one or more support arms 64 toprovide access to an interior of the hood 60 as necessary.

The hood 60 may form an enclosure with a tray 65 below the fetal chamber100 to provide a sealed enclosure thereby isolating the fetal chamber100 from external disturbances such as light, sound or other elementsthat could excite or otherwise disturb the fetus 5, which can bedetrimental to the growth of the fetus 5. The hood 60 may includesealable access ports 62 sized to allow medical professionals to accessthe fetal chamber 100 without lifting the hood 60.

The cart 50 may also include a plurality of therapeutic or diagnosticelements to facilitate treatment of the fetus 5 while the fetus 5 iswithin the fetal chamber 100. For instance, the cart 50 may include anIV pole 80 configured to support an IV bag containing medicationnutrition or other therapeutic solutions to be infused into the fetalchamber 100, amniotic circuit 200 or oxygenation circuit 400.

The tray 65 may include areas configured to organize diagnostic items,such as an ultrasound probe 70 that is connected with an ultrasoundcomputer configured to process the ultrasound image data acquired by theultrasound probe 70. Similarly a bin is provided for a container ofultrasound gel 72, the ultrasound gel configured to facilitate use ofthe ultrasound probe 70 to scan the fetus 5 to monitor the developmentof the fetus 5.

The cart 50 may also include one or more access doors 58 to facilitateaccess to the various components of the system 10, for example theamniotic fluid circuit 200 and the oxygenation circuit 400 whennecessary while limiting access to the components of the system 10 atother times.

The cart 50 further includes a mount for supporting the centralcontroller 700 for the apparatus, which in the present instance is acomputer having a display 710 configured to display operating parametersand alerts and an input/output mechanism to allow the operator to inputdata or control aspects of the process. The input/output mechanism mayinclude one or more input devices, including but not limited to akeyboard, mouse and track pad.

Referring to FIG. 15, the central controller 700 receives signals fromvarious sensors and elements of the system 10 and provides controlsignals to various components to control the operation of the system 10.Specifically, the central controller 700 may receive signals fromsensors such as the gas pressure sensors 522, 532 and in response tothose signals the central controller 700 may control the gas blender 540accordingly. Similarly, the central controller 700 may receive signalsfrom the turbidity meter 350 and control the operation of pump 240.

It will be recognized by those skilled in the art that changes ormodifications may be made to the embodiments described above withoutdeparting from the broad inventive concepts of the disclosure. Forinstance, as shown in FIG. 13, the fetal chamber 100 may include a fluidagitator operable to agitate and/or circulate the amniotic fluid withinthe fetal chamber 100 to minimize stagnate areas in the fetal chamber100. Additionally, as shown in FIG. 16, the amniotic fluid circuit 200may incorporate a circulation loop that circulates amniotic fluid fromthe fetal chamber 100 to a sterilizing element, such as a UV sterilizerand then feeds the amniotic fluid back into the fetal chamber 100.

Referring to FIG. 17, according to one aspect of the disclosure theoxygenation circuit 400 may include a recirculation path configured toprovide an increased flow of blood through the oxygenator 410 to impedethe formation of blood clotting in the oxygenator 410. As shown in theillustrated embodiment, the oxygenator 410 is connected with the fetus 5and the oxygenation line, which includes two fluid lines: the drain line440 and the infusion line 445. Blood flows from the fetus 5 though thedrain line 440 to the oxygenator 410, then the blood flows through theoxygenator 410 and returns to the fetus 5 via the infusion line 445.

The volume of blood flowing through the oxygenation circuit 400 variesbased on the size of the fetus 5. Smaller fetuses have lower blood flowthan older/larger fetuses. When the fetus 5 is small, the lower flow ofblood through the oxygenation circuit 400 may increase areas ofstagnation or low flow in the oxygenation circuit 400, which can lead toclot formation. It may be possible to ameliorate clot formation by usingheparin. However, it may be desirable to avoid or limit the use ofheparin.

To increase the flow of blood through the oxygenator 410, theoxygenation circuit 400 may include a recirculation loop 420. Therecirculation loop 420 is a circulation loop that is parallel to thedrain line 440 and the infusion line 445. The recirculation loop 420 maybe connected with the oxygenator 410 in a variety of ways to allow aportion of the blood in the oxygenation circuit 400 to re-circulaterather than flowing directly to the fetus 5. For example, the oxygenator410 may include a pair of inlet connections and a pair of outletconnections. The recirculation loop 420 may be connected directly to aninlet of the oxygenator 410 and an outlet of the oxygenator 410, whilethe drain line 440 is connected to another of the inlet connectors andthe infusion line 445 is connected with another of the outlet connectorsof the oxygenator 410. Alternatively, the recirculation loop 420 may beconnected with the drain line 440 so that the two lines merge to flowinto the oxygenator 410.

Similarly, the recirculation loop 420 may be connected with the infusionline 445 so that the flow of blood exiting the oxygenator splits, withpart of the blood flow flowing to the fetus 5 via the infusion line 445and part of the blood flow recirculating to the oxygenator 410 via therecirculation loop 420. In either configuration, the flow of blood fromthe outlet of the oxygenator 410 is split so that a portion of the bloodflows to the fetus 5 via the infusion line 445, while a portion of theblood flows through the recirculation loop 420 and then flows back intothe inlet of the oxygenator 410.

To increase the blood flow through the oxygenator 410, the recirculationloop 420 may include a fluid pump 430. The fluid pump 430 may be any ofa variety of pumps configured to pump fluid, including but not limitedto centrifugal pumps and positive displacement pumps, such asperistaltic pumps. The fluid pump 430 provides the recirculation loop420 within an increased flow of fluid relative to the fluid flow throughthe drain line 440 and the infusion line 445. More specifically, thefluid flow through the recirculation loop 420 may be at least twice theflow rate as the flow through the drain line 440 and the infusion line445. For instance, the pump may provide a flow rate of 400 mL/minthrough the recirculation loop 420, while the flow rate through thedrain line 440 and the infusion line 445 may be approximately 100mL/min. In this way, the flow from the recirculation loop 420 and thedrain line 420 combine to provide and increased flow of blood throughthe oxygenator 410. As a result, the increased fluid flow through theoxygenator 410 reduces pooling and stagnant areas within the oxygenator410, thereby limiting the formation of blood clots within the oxygenatorcircuit 400.

Although the flow of blood through the oxygenator 410 is increased, theoxygenation circuit 400 is configured so that the flow rate of bloodreturning to the patient is not increased by the presence of therecirculation loop 420. In other words, the flow of fluid from the fetus5 and returning to the fetus 5 is substantially unaffected by therecirculation loop 420. The fluid pump 430 provides a steady flow offluid into the oxygenator 410 and diverts a substantially equal flow offluid from the outlet of the oxygenator 410. Therefore, the fluid flowto the infusion line 445 that returns to the fetus 5 is substantiallysimilar to the fluid flow from the drain line 445. In this way, thefluid pump 430 is not in line with the fluid flow from the fetus 5 tothe oxygenator 410 so that the fetus's heart primarily controls the flowof blood flowing from the fetus 5 to the oxygenator 410 and returning tothe fetus 5.

By incorporating a recirculation loop 420 to increase the flow of fluidthrough the oxygenator 410, the infusion of heparin into the fetus 5 toprevent blood clots in the oxygenation circuit 400 may be reduced oreliminated. However, for the internal surfaces of the oxygenationcircuit 400 that come into contact with the fetus's blood, it may bedesirable to coat such surfaces with a biologically-active compound thatprevents clot formation.

Referring to FIGS. 19, 20, 23, and 23-38 the system 10 may include oneor more of the fetal chambers 100 in various configurations. Forexample, FIGS. 19 and 20 illustrate an embodiment of the fetal chamber100 having less of a taper at the ends 108 and 109 incorporating furtherconnectors in the fetal chamber 100, such as a connector 160 configuredto connect to an ultraviolet sterilization unit 162.

Referring to FIGS. 23 to 26, the fetal chamber 100 of the system 10 mayinclude a supplemental heating element 164 within the fetal chamber 100configured to heat the amniotic fluid within the fetal chamber 100 tohelp maintain the fluid temperature within a predetermined range. Asillustrated in FIG. 25, the fetal chamber 100 may include a plurality ofrollers 166 that can be driven in a first direction to tilt the cradle610 in a first direction or driven in a reverse direction to tilt thecradle 610 in a second direction.

Referring to FIGS. 27 to 30 the system 10 may include a fetal chamber100 devoid of the rigid frame 110. Instead, the fetal camber 100 is agenerally tubular film 168 having an access opening along one side tofacilitate entry of the fetus 5 into the fetal chamber 100. The accessopening includes a closure such as a slide lock mechanism to provide afluid-tight seal. As shown, the ends 108, 109 of the fetal chamber 100may be supported by hubs 170 that seal off the open ends of the tubularfilm 168 and that also provide access ports for the amniotic fluid inlet142, the amniotic fluid discharge 144, the drain line 440, and theinfusion line 445. The hubs 170 may further include cogs 172 configuredto facilitate rotation of the fetal chamber 100 by corresponding gears.

Referring to FIGS. 31 to 33, the fetal chamber 100 of the system 10 mayinclude a hinged frame and a flexible bag having an access opening tofacilitate entry of the fetus 5 into the fetal chamber 100. A slide lockmaybe provided to seal the access opening and the edges of the bag areconfigured to be clamped between the upper and lower hales of the frameto provide a secondary seal. Displaceable elements, such as solenoidactuator, may be disposed in the corners of the frame. The actuatorsraise and lower the corners of the frame to agitate the fluid within thefetal chamber 100, thereby minimizing stagnant areas in the fetalchamber 100. Referring to FIGS. 34 to 37, the system 10 may includeseparate fluid chambers that can be inflated and deflated to agitate thefluid in the fetal chamber 100.

Referring to FIGS. 39 to 41, the cart 50 of the system 10 may beconfigured as shown in the illustrated embodiments. According to oneaspect of the disclosure, the cart 50 includes a rotatable hood 60 thatencloses the fetal chamber 100. The entire hood 60 may be configured torotate as the fetal chamber 100 is rotated. To facilitate access intothe hood 60, access ports 62 are spaced around each side of the hood 60.

Additionally, as described above the fetal chamber 100 may be configuredto have a variable volume so that the volume can expand as the fetus 5grows. One mechanism described above includes a series of restrictionplates that limit the amount the fetal chamber 100 can expand.Alternatively, the fetal chamber 100 may comprise a reservoir having oneor more dividers that segment the reservoir. The volume of the reservoircan be increased by manipulating or removing one or more of thedividers. In such an arrangement, the wall of the fetal chamber 100 maybe generally rigid rather than having one or more flexible walls.Accordingly, it should be understood that a variety of variable volumefluid reservoirs can be used as the fetal chamber 100.

The singular forms “a,” “an,” and “the” include both single and pluralreferents unless the context clearly dictates otherwise. As used herein,the terms “host,” “subject”, “fetus”, “infant” and “patient” refer toany animal, including mammals, for example but not limited to humans.

The following example is provided to illustrate various embodiments ofthe present disclosure. The example is illustrative and is not intendedto limit the scope of the claims in any way.

An extracorporeal support system was provided using a pumpless circuitcontaining a near zero resistance oxygenator (MaquetQuadrox-ID PediatricOxygenator: Maquet Cardiopulmonary AG, Rastatt, Germany). The animalswere maintained with both systemic antibiotics and antibiotics added tothe fluid, parenteral nutrition modified to a formulation based onsubstrate requirements of premature lambs, sedation as required, andprostaglandin E2 (PGE2) infusions.

Fetal lambs were placed directly on the extracorporeal support systemcircuit after exposure by maternalhysterotomy and connection of theoxygenator in an antegrade orientation, with arterial inflow from acannula placed in the right common carotid artery and venous return viaa cannula in the right jugular vein inserted to the depth of the rightatrium. Once full circuit flow was established, the fetal lamb wasremoved from the uterus and was immersed in an open incubator filledwith fluid, with an electrolyte composition designed to mimic amnioticfluid. No vasopressors were utilized at any time during the runs oncethe lamb was stable on the circuit.

The early gestation fetal lambs were maintained in a fetal chamberformed of a flexible bag, referred to herein as a “Biobag”. The Biobagis a single use, completely closed system having a variable volume thatcan be optimized for the size of the fetus. Additionally, theconfiguration and number of ports, and flow and volume of fluid exchangecan be optimized for a particular fetus. The Biobag was formed out ofsilver impregnated metallocenepolyethylene film and incorporated aparallel circuit containing a UV light chamber for additionalantibacterial effect. The Biobag has an open, sealable side tofacilitate insertion of the fetus at the time of cannulation and has thebeneficial properties of being translucent and sonolucent for monitoringand scanning the fetus. The Biobag was contained within a mobile supportplatform that incorporated temperature and pressure regulation, padding,and fluid reservoirs along with fluid exchange circuitry.

The Biobag was constructed of metallocene polyethylene film (about 80micrometers thick) containing 2% silver cation; the later impartsantimicrobial properties to the film. Prior to heat-welding the bag toshape, several through-wall barbed disc-ports were heat welded to thefilm sheet. There are four barbed ¼″ disc ports (Eldon James:PND4-E8402-QC), four threaded 1″ disc ports (Eldon James:PD38-400-E8402-QC), one barbed ⅜″ disc port (Eldon James:PND6-E8402-QC), and one barbed ⅝″ disc port (Eldon James:PND10-E8402-QC).

The ports were located as shown in FIG. 42. Port A is for inflow ofamniotic fluid. Ports F and G are for an inline ultravioletsterilization circuit (described below). Port C was used to detect fluidenvironment temperature and to remove trapped air from the lumen of theBiobag. Port H sits on the underside of the Biobag and allows amnioticfluid to drain out, along with meconium, urine, and other wastes. Port Chas a 1-2″ length of tubing attaching a Y-connector with a temperatureprobe and clave for air removal. Port D is used to detect bag pressure(described below). Ports B1, B2, E1, and E2 house the Bioline-coatedMaquet ECMO tubing which traverses the wall of the Biobag whilemaintaining sterility. Only one of each of the B-type ports and E-typesports were used for a given patient. Within the bag the ECMO tubing wasconnected to the vascular cannulae (implanted into the carotid arteryand umbilical vein), while outside of the bag the tubing was connectedto the Maquet Quadrox oxygenator. The ECMO tubing was firmly secured tothe Ports B and E using compression fittings secured to the threaded 1″port discs. Ports A, F, and G have a nylon quick-connect male fitting(http://www.mcmaster.com/#catalog/120/222/=tfgyvp) attached to the discports with a 1-2″ length of tubing(http://www.coleparmer.com/Product/Masterflex PharMed BPT Tubing L S 1525/EW-06508-15).

A high accuracy (+/−0.1 degree C.) thermistor probe(http://www.adinstruments.com/products/nasaltemperature-probes) waspositioned within the bag and exits via port C. The thermistor connectsto a temperature pod(http://www.adinstruments.com/products/temperature-pods) which itselfwas attached to an analog to digital converted(http://www.adinstruments.com/products/powerlab) connected to a windows7 based PC running digital data logging software (LabChart, Version 7 or8; http://www.adinstruments.com/products/labchart).

Amniotic Fluid Components: The ingredients for artificial amniotic fluid(sodium chloride, sodium bicarbonate, potassium chloride and calciumchloride dissolved in distilled water) are designed to mimic the ionicconcentrations (Na+ 109, Cl− 100, HCO3− 20, K+ 6.5 and Ca2+ 1.6 mmol/L)and pH (7.0) of fetal sheep amniotic fluid. Ingredients are laboratorygrade chemicals purchased from commercial vendors.

Batches of amniotic fluid (about 340 L) were mixed and filter sterilized(0.22 micrometers;http://www.emdmillipore.com/US/en/product/Standing-Stainless-Steel-Filter-Holders-%2890-and-142-mm%29, MM NF-C743) into heat-sterilized custom polypropylene carboys usinga peristaltic pump. The process took about 60 minutes.

Delivery to Biobag. Sterile tubing from the glass carboys was connectedto a peristaltic pump. After leaving the pump, the amniotic fluid passesthrough two in-line 0.22 filter cartridges(http://www.emdmillipore.com/US/en/product/WEllipak-Disposable-FilterUnits,MM_NF-0523), and then through a stainless-steel heat exchanger tobring the fluid up to 39.5 degrees C. before being pumped into theBioBag. An ultrasonic clamp-on tubing flow probe and meter(http://www.transonic.com/search/?Keywords=ht110&display=search&newSearch=true&noCache=1)are used to monitor the rate of fluid deliver to the Biobag (about 50ml/min). Amniotic fluid exits the Biobag by way of Port H located on thelower surface of the Biobag. A pressure device is incorporated into PortD to maintain pressure within the Biobag at about 8 to 10 mm Hg (normalamniotic fluid pressure in vivo). Waste amniotic fluid passes through asterile trap prior to being sent to a floor drain. The Biobagtemperature, pressure and amniotic flow were recorded on digital datalogging software.

UV sterilization loop: In the current design, a peristaltic pumprecirculates amniotic fluid in the Biobag (about 100 ml/min) throughports G and H after passing through an in-line, ultravioletsterilization unit(http://www.mcmaster.com/#ultraviolet-water-purifiers/=tthkg0; catalog#8967T22). The device has broad spectrum antimicrobial properties.

Biobag heat regulation: In the current design, the Biobag rests atop acustom-designed aluminum water-heated plate to provide effective heattransfer via conduction. The heat plate is connected to a digitallycontrolled, recirculating water heater. A fluid-filled mattress sitsatop the heat plate for greater heat control and cushioning for theanimal. The heat plate, fluid cushion, and Biobag are placed within a 32inches by 24 inches container that is covered by an insulating,transparent polycarbonate cover.

Fetal cardiopulmonary monitoring: Blood pressure was continuouslyrecorded via ports on either side (i.e. arterial and venous limbs) ofthe Maquet oxygenator using clinical disposable pressure transducers(http://www.icumed.com/products/critical-care/pressure-monitoring-system/transpac.aspx)connected to a bridge amplifier(http://www.adinstruments.com/products/bridge-amps) attached to thedigital data logging system. Raw pressure signals are processed tocalculate systolic and diastolic pressure, heart rate and the pressuredifference across the oxygenator. An ultrasonic clamp-on tubing flowprobe and meter(http://www.transonic.com/search/?Keywords=ht110&display=search&newSearch=true&noCache=1)were used to monitor the rate of blood flow to the patient.

The Biobag was used to apply extracorporeal support to earliergestational fetuses. At earlier gestational ages (114 to 120 daysgestation), we noticed greater instability at the time of cannulationand transition to the extracorporeal support system circuit resulting inbradycardia and sometimes asystole requiring atropine and epinephrine.Once on the circuit, diminishing circuit flows and progressive edema andelectrolyte imbalance were encountered within a few days of cannulationnecessitating a re-assessment of the physiology. In the normal fetus,there is preferential streaming of “oxygenated” umbilical venous returnacross the foramen ovale to the left sided circulation due to acombination of directed streaming of blood from the ductus venosus andthe anatomic orientation of the foramen ovale.

In our system, return of oxygenated blood was via the superior venacava. We postulated that this resulted in less efficient right to leftflow of umbilical venous return, resulting in increased right-sidedvenous pressure. We also speculated that the acute increase inright-sided venous pressure, combined with the normally lower systemicblood pressure in earlier gestation lambs, would result in initialinstability with subsequent reduced perfusion pressure across themembrane resulting in decreased flows, and eventually inadequate oxygendelivery in younger animals. We confirmed that right-sided venouspressures were elevated (measured abdominal IVC pressures 9.6+2 mm Hgvs. 4+2 mm Hg in normal fetuses) in the carotid artery and jugular veincannulated animals and explored two solutions.

Our first approach was to utilize Angiotensin II, the primary vasoactiveagent during mid-gestation that is present in high concentrations in theplacenta, to increase systemic blood pressure and maintain perfusionpressure across the membrane. While instability during transition wasstill an issue requiring epinephrine, stability and circuit flowsthereafter were much improved by a continuous angiotensin II infusionwhich could ultimately be tapered off after approximately 1 week onextracorporeal support system as systemic pressures increased. The otherapproach was utilization of the umbilical vein for venous return. Whilewe initially used the jugular vein because of concern about umbilicalvenous spasm, we were able to cannulate the vein using a minimalmanipulation technique with topical papaverine irrigation. The cannulawas advanced to a position with the tip just inside the abdominal fasciaand secured using a silastic cuff attached to the abdomen.

Umbilical cannulation immediately eliminated the instability during thetransition to the extracorporeal support system circuit. Sinceinitiation of the umbilical venous drainage approach, cannulationinstability was significantly reduced and/or eliminated; there was noneed for epinephrine, and no need for gradual initiation of circuitflow. We then opened flow to the oxygenator and immediately occluded theumbilical cord. Right-sided pressures were normal, there was animprovement in flow, and more efficient right to left transfer ofoxygenated blood as demonstrated by increased carotid artery oxygensaturations and improved oxygen delivery. This approach thereforeutilizes umbilical venous return with occasional Angiotensin II infusionto support systemic blood pressure, if such support is needed.

These procedures provided stable support of three lamb fetuses at 110 to113 days gestation for up to 21 days on extracorporeal support system.From the perspective of lung development lambs at 110 to 113 daysgestation are in the mid to late cannalicular phase of lung development,which is the biological equivalent of the 23 to 24 week gestationpremature fetus. All three lambs demonstrated complete hemodynamicstability and stable physiologic parameters with grossly normal growthand development. After 21 days he was transitioned to mechanicalventilatory support with stable blood gases (7.48/46.7/132/99%) onminimal ventilator settings (SIMV, FiO2 30%, PIP 15 cm H20, CPAP 5 cmH20, Rate 20). He was weaning on ventilator support when he developedmarked abdominal distention, respiratory decompensation, and waseuthanized. He was subsequently found to have anileal intestinalobstruction due to what appeared to be inspissated meconium. The lungsappeared well developed and mature on histologic assessment with someevidence of ventilation induced injury.

These results demonstrate that extreme premature fetal lambs,corresponding biologically to a 23 to 24 week gestation premature fetus,can be supported in the extracorporeal support system for up to 3 weekswithout apparent physiologic derangement or organ failure. This is instark contrast to previously published results of attempted prolongedextracorporeal support of the fetus that have been uniformly associatedwith progressive cardiac failure and metabolic deterioration. The lambsare remarkably stable on the extracorporeal support system, maintainfetal circulatory pathways and metabolic parameters, and demonstrateevidence of normal maturation and growth. In addition, we havedemonstrated transition to postnatal life with normal long-term survivalafter prolonged extracorporeal support.

There are a number of features of the current extracorporeal supportsystem that contribute to this success. The first is an extremely lowresistance oxygenator incorporated in a pumpless circuit with lowsurface area and priming volumes, connected to the fetal vasculature inan arterial to venous orientation. This system is comparable to thehemodynamics of the placenta itself as evidenced by the priming volumesand flows generated in our circuit. The reported placental blood volumeof the sheep is 23.1 to 48.1 ml/kg, with normal placental blood flowreported as 199+/−20 ml/min/kg. Our circuit requires a priming volume of80 to 90 ml, or 27 ml/kg for an average 120 day 3 kg fetal lamb, andflow rates in our system ranged from 90-140 ml/min/kg over our range ofgestational ages. Although the flow rates are slightly less than thenormal placenta, gas exchange via the oxygenator is highly efficient andnear normal fetal blood gases and oxygen saturations can be maintainedwell within the sweep gas parameters of the oxygenator.

In addition, the pumpless design of the circuit allows for some degreeof “autoregulation” of circuit flow by the fetal heart and vasculature.Flow in our circuit is dependent upon the size of the cannulas and thepressure gradient across the circuit. Our lambs consistentlydemonstrated the ability to increase blood pressure and flow in responseto induced hypoxia by increasing systemic blood pressure. A secondfeature of the system is the fluid environment. The fetus in theextracorporeal support system demonstrates unimpeded fluid breathing andswallowing analogous to normal fetuses. This has resulted in normal lungdevelopment and maturation by histologic and functional criteria. Athird feature is our improving ability to maintain a sterile amnioticfluid environment. The development of the Biobag with its closed designand antimicrobial features was a step forward and we aim to ultimatelydevelop an entirely antibiotic free system. Finally, the ability toeliminate heparin reduced clinical concern related to hemorrhagicevents.

Although we have applied the system to a biologically equivalentpremature fetus, the 110 day fetal lamb is considerably larger (1.5-2kg) than an extremely low birth weight premature fetus. The sizeequivalent fetal lamb is approximately 80 to 93 days (350 to 750 grams)and significant modifications of circuit design may be required.Antisepsis improvement is desired as well as the avoidance ofconventional pharmacologic antibiotics. We have made major strides inthe design of the extracorporeal support system and have seen noinfection in the Biobag animals with systemic antibiotics.

It should be realized that extreme premature delivery is onlyanticipated 50% of the time. While a delivery directly from the uterusto the extracorporeal support system is the ideal, if a fetus could bebriefly supported after delivery and placed onto extracorporeal supportit would markedly expand application of this technology. This would ofcourse require not only maintenance of a sterile system, but the abilityto clear contamination from the system.

Finally, the implications of the extracorporeal support system extendbeyond clinical application, and provide a model for addressingfundamental questions regarding the role of the placenta in fetaldevelopment. Long-term physiologic maintenance of a fetus amputated fromthe maternal-placental axis has now been achieved, making it possible tostudy the relative contribution of this organ to fetal maturation. Thesystem can also be used to bridge the transition from fetal to postnatallife, which may be applied to models of congenital lung disease toexpand the window of opportunity for therapeutic interventions. Theextracorporeal support system therefore represents a capability that hasnot been previously available for research in fetal physiology, andrepresents a powerful new resource for numerous translational clinicalapplications.

In light of the foregoing, it should be understood that this disclosureis not limited to the particular embodiments described herein, but isintended to include all changes and modifications that are within thescope and spirit of the disclosure as set forth in the claims.

The invention claimed is:
 1. A method of using an extracorporeal systemto support a human premature fetus in an extrauterine environment andmaintain the human premature fetus during maturation, the methodcomprising the steps of: positioning the human premature fetus in afetal chamber including a first portion having a rigid first framehaving a first perimeter lip defining a first opening for the firstportion, a second portion having a rigid second frame having a secondperimeter lip defining a second opening for the second portion, whereinbefore said positioning step first moving the first and second portionsof the fetal chamber relative to each other to separate the first andsecond perimeter lips to accommodate the positioning of the humanpremature fetus into the fetal chamber; connecting the premature humanfetus to an oxygenation circuit including connecting a drain lineconfigured to transport blood from the human premature fetus to anoxygenator and connecting an infusion line configured to transport bloodfrom the oxygenator to the human premature fetus; oxygenating blood fromthe premature human fetus via the oxygenation circuit by flowing theblood through the drain line into the oxygenator and from the oxygenatorinto the premature human fetus through the infusion line whereby theoxygenator provides oxygen to and removes carbon dioxide from the bloodand wherein the blood flow from the premature human fetus through thedrain line, into the oxygenator, and through the infusion line back intothe premature human fetus is propelled by the premature human fetus thusforming a pumpless circuit; closing the fetal chamber after thepremature human fetus is positioned within the fetal chamber by movingthe first and second perimeter lips together and latching a plurality oflatches located proximate to the first and second perimeter lips tocreate a liquid-tight seal between the first and second perimeter lipsin a closed position for the fetal chamber; injecting synthetic amnioticliquid through an inlet line into the closed fetal chamber to fill thefetal chamber with the synthetic amniotic liquid and immersing thepremature human fetus in the synthetic amniotic liquid within the fetalchamber whereby the synthetic amniotic liquid in the fetal chamber isprevented from passing between the first and second perimeter lips;periodically discharging a used synthetic amniotic liquid from the fetalchamber and injecting fresh synthetic amniotic liquid into the fetalchamber; wherein the fetal chamber is positioned upon a cart wherein thecart has a hood; and positioning the hood such that the hood inconjunction with the cart encloses the fetal chamber.
 2. The method ofclaim 1 wherein the fetal chamber has an expandable inner volume and themethod includes the step of expanding the inner volume of the fetalchamber without opening the fetal chamber in response to growth of thepremature human fetus.
 3. The method of claim 2 wherein the fetalchamber has a length greater than a width.
 4. The method of claim 2wherein the extracorporeal system further includes a central controllercomprising a computer having a display.
 5. The method of claim 4 whereinthe extracorporeal system further includes a control valve and a fluidflow meter on the inlet line and further comprising using the centralcontroller to regulate flow of the fresh synthetic amniotic liquid intothe fetal chamber by controlling the control valve in response to inputfrom the fluid flow meter.
 6. The method of claim 4 wherein theextracorporeal system further includes an outlet line from the fetalchamber to carry the used synthetic amniotic fluid from the fetalchamber and a discharge pump on the outlet line and further comprisingusing the central controller to control the discharge pump to controlthe flow of the used synthetic amniotic fluid from the fetal chamber. 7.The method of claim 6 further comprising the step of using the dischargepump to withdraw an amount of the used synthetic amniotic fluid from thefetal chamber to maintain a fluid pressure in the fetal chamber within adesired range.
 8. The method of claim 6 further comprising the step ofactivating the discharge pump to remove the used synthetic amnioticfluid from the fetal chamber in response to sensed turbidity in thefetal chamber.
 9. The method of claim 2 further comprising the step ofpriming the drain line and the infusion line with maternal or fetalblood prior to connecting the premature human fetus to the oxygenationcircuit.
 10. The method of claim 9 further comprising the step of liningthe drain line and the infusion line with anti-clotting compounds. 11.The method of claim 2 wherein the extracorporeal system further includesa fluid pressure sensor on the drain line and a fluid pressure sensor onthe infusion line and wherein the method further comprises monitoring afluid pressure drop over the oxygenator.
 12. The method of claim 11wherein the extracorporeal system further includes a fluid flow meter onthe infusion line and wherein the method further comprises monitoringthe fluid flow rate of blood returning to the premature human fetus. 13.The method of claim 2 further comprising the step of rotating the fetalchamber with the premature human fetus in the fetal chamber.
 14. Themethod of claim 2 further comprising the step of tilting the fetalchamber with the premature human fetus in the fetal chamber.
 15. Themethod of claim 2 wherein the cart further includes a support armattached to the hood and the method further comprises the step oftranslating the hood upward away from the fetal chamber to expose thefetal chamber by moving the hood along the support arm.
 16. The methodof claim 4 wherein the method further includes the step of using thecontroller to control a flow rate of oxygen and air into the oxygenator.17. The method of claim 4 wherein the cart includes a mount forsupporting the central controller and further comprising the step oftransporting the cart with the fetal chamber containing the prematurehuman fetus from an operating room to a neonatal care center.
 18. Themethod of claim 17 wherein the cart includes a portable amniotic tank ofthe fresh synthetic amniotic fluid in fluid communication with the inletline and the method further comprises injecting the fresh syntheticamniotic fluid from the portable amniotic tank into the fetal chamber.19. The method of claim 2 wherein the fetal chamber includes a one-wayflow valve impeding liquid flow from the fetal chamber, and the methodfurther comprises the step of inserting a suction device through theone-way flow valve into the fetal chamber.